1. Field of the Invention
The present invention relates to an engine and a straddle-type vehicle including the engine.
2. Description of Related Art
FIG. 9 is a cross-sectional view of a typical engine 100 as disclosed in Japanese Patent Application Laid-Open No. 2006-307827. The engine 100 includes a crankcase 101, a body cylinder 102 and a head cylinder 103. As shown in FIG. 9, a piston ring 105 of a piston 104 is normally and always located at a higher position than a position of the crankcase 101. Even when the piston 104 reaches a bottom dead center, the piston ring 105 is located at a position higher than that of the crankcase 101. Due to this, it is necessary to set a length of an upper section 102a that belongs in a head cylinder 103 and is located at a higher position than that of the crankcase 101 to be larger than a stroke length of the piston 104.
Meanwhile, the head cylinder, body cylinder and crankcase are generally joined integrally by a bolt. Therefore, if the distance between the head cylinder and the crankcase is long, as seen in FIG. 9, a longer bolt is required. The engine tends to increase in weight as the bolt is longer.